Conventionally, there has been known a technology to encrypt a target data piece included in a job from a security point of view, by using an external recording medium holding a public key and a secret key and having the function for decrypting data with this secret key, when the job is transmitted to an image processing apparatus, such as a MFP (Multi Function Peripheral) that is a multifunctional digital machine, from a personal computer (hereinafter will be referred to as “PC”) that is a user (client) terminal connected to a network.
To explain in other words, different shared keys are generated for respective data pieces by the PC. And a target data piece is encrypted with its shared key and this shared key is encrypted with a public key of the external recording medium. The encrypted target data piece and shared key are transmitted to the image processing apparatus. When the recording medium is connected to the image processing apparatus receiving the encrypted target data piece and shared key, the encrypted shared key is decrypted by the external recording medium with a secret key thereof. With this decrypted shared key, the target data piece is decrypted, and then the job is executed.
This technology appears in concrete form in Japanese Unexamined Laid-open Patent Publication No. 2005-348250, as follows. An image processing apparatus encrypts a target data piece with a shared key, encrypts this shared key with a public key, and stores the encrypted target data piece and shared key with their connection. When the job data is printed out, the encrypted shared key is transmitted to an IC card holding a secret key, and the shared key decrypted with this secret key is obtained therefrom. With this decrypted shared key, the encrypted job data is decrypted.